teuthology/misc: support MappingProxyType in deep_merge
teuthology/misc: support MappingProxyType in deep_merge

Signed-off-by: Patrick Donnelly <d35c2028e065409a3eff47e1b4cba347a9379b4b@redhat.com>

ktdreyer/teuthology,ceph/teuthology,ceph/teuthology,ktdreyer/teuthology